She doesn't want to admit that they had the information about Al Qaida plotting to crash planes into buildings and planning attacks in the U.S. simply because this stuff wasn't differentiable from the gazillions of other snippets of intelligence that the CIA and FBI are always getting, until after the fact. They are simply to arrogant to own up to the limits of our own capabilities to act outside of public approval in a democracy.
The irony is, nobody can really make the case that there is anything that either the Clinton administration NOR the Bush administration could, pragmatically, have done to stop 9/11. The reason isn't that there wasn't anything we could do, it's that there was nothing we could have done that would have been politically sellable pre-9/11. In the midst of peace-time, we couldn't justify overthrowing Afghanistan, and causing the turmoil that would likely get Pakistan's gov't taken down in an insurrection as well, absent convincing proof of an imminent threat. I certainly accept that. What I DON'T accept is that the current administration is so busy spinning and trying to discredit Clarke (who, of course, ALSO admitted that 9/11 could not have reasonably been prevented) because they were so busy extending their POST 9/11 mandate so that it would cover not just an overthrow of Afghanistan, but also of Iraq, despite the fact that there was NEVER any linkage between Al Qaida and Iraq. The irony, of course, is that Saddam had effectively kept Al Qaida from operating in Iraq, and once he was out of power, the vaccuum was such that Al Qaida could ONLY THEN begin to use Iraq as the replacement base of operations which they needed after losing the Taliban regime in Afghanistan.